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mov     ah, UpDownFlag   ; 00h for down stroke, 80h for up stroke
mov     al, VirtualKey   ; Windows virtual-key code
mov     bh, PrefixFlag   ; 00h if no prefix, 1 if 0E0h prefix byte
mov     bl, ScanCode     ; hardware scan code
 
mov     si, word ptr [ExtraInfo]
mov     di, word ptr [ExtraInfo+2]
                         ; extra information
 
call    [Keyboard_Event]    ; keyboard-event function
 
The Keyboard_Event function records a keystroke. The keystroke may
subsequently be used to generate a WM_KEYUP or WM_KEYDOWN message.
 
The keyboard driver's interrupt handler calls this function.
 
Parameter   Description
────────────────────────────────────────────────────────────────────────────
 
UpDownFlag  Specifies whether the key is up or down. The parameter is 0x00h
            for a down stroke and 80h for an up stroke.
 
VirtualKey  Specifies a virtual-key code. The code must be a value in the
            range 1 to 254.
 
PrefixFlag  Specifies whether the scan code was preceded by the 0E0h prefix
            byte. The parameter is 00h if there was no prefix byte, and is 1
            if there was a prefix byte.
 
ScanCode    Specifies the hardware-scan code for the key.
 
ExtraInfo   Specifies an additional 32-bit value associated with the key
            stroke.
 
Return Value
 
This function has no return value.
 
Comments
 
Although the keyboard driver passes the hardware-scan code (which is
OEM-dependent) to Windows, Windows does not use the code. Instead, Windows
subsequently passes the scan code to the ToAscii function, which may use it
for special purposes. The interrupt handler sets the up/down bit in the scan
code to 0.
 
This interrupt handler may process some keystrokes without passing them to
Windows through the keyboard-event callback function. In particular, the
handler processes CTRL+ALT+SYSREQ keytrokes and generates a nonmaskable
interrupt (NMI). Under certain circumstances, the driver's interrupt handler
passes keystrokes to the original keyboard-interrupt handler. This is the
case for CTRL+ALT+DELETE key combination and for the PAUSE key.
 
Use the PRINTSCREEN key to take a screen snapshot, which is saved in the
Windows clipboard. This is handled in the interrupt routine by calling the
event procedure with VK_SNAPSHOT in the AL register, with the value equal to
0 (for full-screen snapshot) or 1 (for active-window snapshot) in the BL
register.
 
See Also
 
Enable
 
 
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